The present invention relates to devices for dispensing and metering liquid or pasty products, such as liquid soaps, cleaning pastes, and the like.
In general, devices of this character are adapted to be associated or coupled with a detachable reservoir containing the product to be dispensed. The body of this device comprises an internal dispensing chamber communicating through a pair of valves on the one hand with the orifice opening into the reservoir and on the other hand with the outlet nozzle. A suction and delivery piston actuated by means of an external control push member is fitted in said chamber. The outlet nozzle is advantageously disposed on the head of said push member having like the piston a hollow stem or rod.
During the operative or delivery stroke of the piston a metered amount of product contained in said chamber is strongly compressed. Now, the valve arrangement is such that this compression opens the outlet valve and keeps the inlet valve in its closed or seated position. Therefore, this action causes the metered amount of product contained in the dispensing chamber to be ejected through the outlet nozzle.
On the other hand, when the piston is returned to its normal or inoperative position by spring means provided for this purpose the valve associated with the outlet nozzle remains closed while the valve controlling the communication with the inner space of the reservoir is open. Consequently, a predetermined quantity of product is sucked into the chamber of the device. Therefore, this suction takes place immediately when releasing the control push member, so that the corresponding metered amount of product remains in a waiting condition in said dispensing chamber until the device is actuated again.
In a known arrangement the dispensing and metering device comprises a bellows-like tube associated with the control push member. It is obvious that this device cannot operate properly for dispensing relatively thick creams, inasmuch as the bellows may further undergo undesired and detrimental distortions in actual service.
Thus, a known inconvenience of these prior art devices is that their operation cannot be fully satisfactory. On the other hand, their useful life is estremely short, since they become useless after a relatively short service time.
This is due to the fact that in many cases a poor fluid tightness is observed around the control piston due to a failure or, more generally, a premature wear of the piston seal. In fact, this piston seal wears out very rapidly, notably when the product to be dispensed contains abrasive substances as in many applications.
Under these conditions, apparatus or devices of this type become rapidly useless.